North Dakota is no longer the only state to have its same-sex marriage ban go unchallenged: Seven couples on Friday filed suit in federal court in Fargo seeking to overturn a 2004 voter-approved amendment to the state's Constitution prohibiting the practice.

The Associated Press reports:

"The lawsuit, filed in U.S. District Court in Fargo, challenges both North Dakota's constitutional ban on gay marriage and its refusal to recognize marriages of same-sex couples who legally wed in other states. That means cases are currently pending in all 31 states with gay-marriage bans. Judges have overturned several of those bans since the U.S. Supreme Court struck down part of the federal Defense of Marriage Act last year."

In the lawsuit, plaintiffs said North Dakota "will incur little to no burden in allowing same-sex couples to marry and in recognizing the lawful marriages of same-sex couples from other jurisdictions on the same terms as different-sex couples."

It said the state's ban, approved a decade ago by nearly three-quarters of voters, subjects same-sex couples seeking to marry to "an irreparable denial of their constitutional rights."

"In light of the decision of some county clerks to issue marriage licenses to same-sex couples, I will be filing emergency motions in the federal courts to stay Judge Crabb's order," Van Hollen wrote in a statement.

"The United States Supreme Court, after a referral from Justice Sotomayor, stayed a lower court's decision striking down Utah's ban on same-sex marriage," the attorney general noted. "There is no reason to believe the Supreme Court would treat Wisconsin's ban any differently."

Update at 6:00 p.m. ET. Judge Strikes Down Wisconsin Gay Marriage Ban

A federal judge on Friday also struck down Wisconsin's ban on same-sex marriage, calling it unconstitutional.

Judge Barbara Crabb's decision makes Wisconsin the 27th state where same-sex couples can marry under law or where a judge has ruled they ought to be allowed to wed, the AP reports.

Carl Tobias, a professor at the University of Richmond School of Law, says the 88-page opinion in the case "is one of the most comprehensive and careful of the dozen or so federal district court opinions to date.

"Judge Crabb thoroughly evaluates all of the relevant issues, clearly articulates the applicable law, fairly addresses both sides of the issues and finds that the Wisconsin ban violates the 14th amendment's due process and equal protection clauses," he says.